An antenna is a device designed for the purpose of emitting or receiving electromagnetic waves towards open space. While a transmitter antenna transforms voltages into electromagnetic waves, a receiver antenna performs the reverse function. The traditional classification of antennas is essentially based on the manner in which the electromagnetic field is distributed in the antenna itself or on the technology used, although classifications can also be made from a more practical point of view, based on their features and technology, their specific uses and their operation.
In the case of antennas with a reflector, the manner of producing and receiving electromagnetic waves is done through one or more reflective surfaces, also known as reflectors. If a large main reflector and/or large focal distance involving large distances to the focus needs to be used, then one or more secondary reflectors or subreflectors are normally used, apart from the main reflector. Whereas the main reflector reflects the incident radiation towards the primary focus, the secondary reflector or subreflector has one focus in common with the parabolic reflector and forwards the electromagnetic waves to the secondary focus.
Thus, the present invention relates to reflective elements (main reflector and/or subreflectors) of the antennas on board telecommunications, radar, radiometer, radio telescope and Earth observation satellites, as well as for other applications. When the reflective elements are made of a composite, the loss of reflectivity (reflectivity being the ability of reflective surfaces to reflect the incident radiation thereon) increases as the frequency increases. Therefore, depending on the work frequency of the mentioned antennas, the reflectivity of their reflective surfaces must be high enough so as to not cause losses which unacceptably degrade the features of said antennas.
In many applications, instead of using metallic materials to construct the reflective surfaces, composites formed by a fiber (carbon, glass, quartz, etc.) and a resin matrix are used. These materials have either an intrinsically low reflectivity (quartz, glass) or a reflectivity which deteriorates to unacceptable values for high frequencies (from 15 GHz or 20 GHz) due to the ohmic losses occurring when carbon fiber is used as a composite, both if this carbon fiber is painted or unpainted, it being necessary to consider solutions improving the reflectivity of these surfaces.
One of the processes used today for improving the reflectivity of antenna reflectors made of a composite consists of arranging a metallized layer (process referred to as metallization) on said reflectors. The reduction in the loss of reflectivity is a function of the temperature, of the purity of the metallized layer and of the thickness thereof.
Multiple methods of metallization are known which can be applied to components manufactured of composites, as is the case of antenna reflectors, particularly for satellites. These methods can be included in three groups: physical methods, chemical methods and others.
The physical methods can in turn be sub-divided into two groups: metal spraying processes and vacuum deposition processes. The metal spraying can in turn be performed by several techniques (flame spraying, electro spraying and plasma spraying). They all essentially consist of raising the temperature of the metal to be deposited above the melting temperature thereof, subsequently projecting the resulting particles by means of special guns. Vacuum deposition can also use several techniques (vaporization, sputtering and ion plating), atoms of metal or vaporized metal being deposited in all of them on the substrate to be metallized in a vacuum environment.
The chemical methods in turn include several processes, such as auto-catalytic coating, electrodeposition and chemical vapor deposition. Auto-catalytic coating consists of activating the surfaces to be metallized such that metal ions generated in a solution prepared for such purpose are deposited thereon. Electrodeposition consists of depositing a metal on a surface upon passing a current in a bath in which the surface to be metallized is introduced.
Within other methods processes not covered by the previous classifications are considered, such as gluing thin sheets of metal either continuously or in strips.
Out of all the mentioned methods, the method which has been used in spatial applications, specifically for satellites, until now has been the vacuum deposition method. This technique has, however, serious drawbacks and limitations, as it is an expensive technique requiring the use of very sophisticated installations, there being virtually no installations of this type for large sizes, the few existing installations furthermore being non-industrial, rather being of a scientific institution, which has limited their use to very specific cases, such as that of telescope mirrors on board satellites.
In addition, the vacuum deposition metallization technique commonly used, in which the material with elevated conductivity is mainly aluminum, produces very thin and very sensitive metallization depositions arranged on the outer face of the surfaces, these metallization layers being very easily damaged, even when cleaning the surfaces, the metallization layer in many cases being removed when the process of cleaning said surfaces is performed. In the event that the metallization layer is damaged, it is necessary to remove the entire arranged layer and again perform the metallization process once more, which involves a very high cost.
The present invention is aimed at solving the previously mentioned drawbacks.